1. Field of the Invention
The present invention is directed to a method and arrangement for adapting a fuzzy controller to different operating points and/or modified system parameters, and in particular to a method and arrangement for adapting a sliding mode fuzzy controller to changes of this type, which represent destabilizing or stability-affecting changes for this type of fuzzy controller.
2. Description of the Prior Art
In complex control-oriented problems, efforts are made to operate controllers in a manner which simulates control strategies of a human expert. Fuzzy controllers have proven especially suitable for such applications because they are simple to program in the form of if-then rules. Since this type of problem formulation approaches the human expert, complex control relationships can also be well-managed with fuzzy controllers. Since fuzzy controllers can also be economically produced on an industrial scale and no complicated mathematical analyses are required for their programming, they have gained entrance into many technical fields of industry. Particularly in the areas of consumer products, more efficient or energy-saving devices can often be built employing fuzzy technology.
The parameters of the system or process to be controlled, and thus of such a fuzzy control system as well, can change dependent on time due to aging or other external influences. Adaptation of the controller with the assistance of an adaptation block is available as a solution for this problem. Various adaptation versions, their advantages and disadvantages, and examples of such adaptation versions have been investigated by the Gesellschaft fur Me.beta.-und Automatisierungstechnik (GMA). They are summarized in the article, "Adaptive Regler, Erlauterungen und Beispiele", VDE/VDE Guideline 3685 dated 1992.
The sliding-mode fuzzy controller represents a special type of fuzzy controller and is distinguished by its special stability properties. The fundamentals and the structure of such a fuzzy controller are disclosed in the PCT Publication WO 93/11 473. These shall be supposed to be known to those of ordinary skill in this field. Such sliding mode fuzzy controllers in diagonal form are equivalent to sliding-mode controllers with a boundary layer. The sliding mode fuzzy controllers can be interpreted by their non-linear transfer characteristic. The balancing of the various possible parameters of such a fuzzy controller for optimum operation is complicated and time-consuming. The adaptation of such a sliding mode fuzzy controllers with a boundary layer to different operating points or modified system parameters (destabilizing stability-affecting changes or system behavior affecting) therefore represents an especially complex problem. The control parameters of sliding mode fuzzy controllers are discussed by R. Palm in the article, "Robust Control by Fuzzy Sliding Mode", in Automatica, pages 1429 through 1437, 1994.